import java.util.HashMap;
import java.util.Map;

/**
 * Created with IntelliJ IDEA.
 * Description:
 * User: Hua YY
 * Date: 2025-03-14
 * Time: 11:08
 */
public class Test100 {
    public static void print(String ss){
        int n = ss.length();
        Map<Character,Integer> hash = new HashMap();
        for(int i = 1 ; i < n ; i++){
            int index = 3*i-1;
            char ch = ss.charAt(index);
            if(3*i-1 < n && !hash.containsKey(ch)){
                System.out.print(ch);
                hash.put(ch,1);
            }
        }

    }

    public static void main(String[] args) {
//        String ss = "它能让构造简单、可靠且高效的软件变得容易";
        String ss = "aaaaaaaaaabbbbbfffffff";
        print(ss);
    }
}
